The present invention relates to a method and apparatus for forming a plastic article having multiple layers including an extrusion body and an overlay or top layer having a varying thickness. More specifically, the present invention relates to an automotive trim strip and to a method and apparatus for extruding such trim strip. The trim strip has an extrusion body intended to face toward the vehicle which is formed of relatively inexpensive thermoplastic material and an outer or overlay layer intended to be viewed which is formed of a second and relatively more expensive thermoplastic material, with the outer layer having a color different from that of the extrusion body and a varying thickness to provide a shaded color appearance on the viewing surface.
In the manufacture of plastic automotive trim strips, it is frequently desirable to have an outer layer which is visible for viewing formed of a material having an enhanced aesthetic appearance over that of the material from which the extrusion body is molded. Thus, the extrusion body will frequently be formed of an economical resin such as a polyvinylchloride (PVC) resin or a polyolefin resin while the overlay layer may be formed of a more expensive type of PVC or polyolefin or other thermoplastic with colorants or other additives mixed therein to enhance the appearance or with various types of laminates including metallic foil, lacquers, Mylar.RTM. films or other types of materials. For example, U.S. Pat. No. 4,600,461 discloses a method and apparatus for producing an extruded plastic material having an inner foamed thermoplastic cellular core and an outer non-porous plastic skin extending along at least one side of the core. Under the invention disclosed in that patent, a foamable thermoplastic material is extruded through a first die outlet to produce a foamed thermoplastic material and, thereafter, a film of non-porous thermoplastic material is applied to at least one side of the extruded foamed material. The extruded foamed material with the non-porous film is then fed through a forming die which shapes and seals the materials into the desired cross-sectional shape.
U.S. Pat. No. 4,832,960 discloses a device for feeding an extrusion head for extruding an elongated product of plastic material having a extrusion body of one type or color of plastic and a surface layer of a different type or color of plastic. The device is designed to permit the surface layer to be selectively fed from one of two additional sources of plastic material, each of which may be of a different type or color from the plastic material forming the extrusion body and a different type or color from the other to provide an elongated article having a extrusion body with alternating colors of overlayers.
U.S. Pat. No. 3,471,898 discloses apparatus for extruding a plastic strip from two sources of different colored thermoplastic material to form a unitary strip having a multicolor appearance.
U.S. Pat. No. 4,772,195 discloses a distributing device for the manufacture of multilayer sheets in which superimposed layers of thermoplastic or other materials are simultaneously extruded and united before being introduced into a die. According to that invention, the distribution of the material of each layer on the surface of the adjacent material may be changed by a modification of the relative viscosity of the materials by adjustment of the temperature of the materials introduced. The invention therein disclosed permits a modification of the cross-sectional shape of the stream of one of the thermoplastic materials in the central channel in order to obtain the desired distribution of such material in the sheet at the outlet of the die.
U.S. Pat. No. 4,349,592 discloses a laminated trim strip formed of an extruded thermoplastic elastomer which is laminated to a tie sheet using conventional extrusion laminating techniques. If the extruded elastomer is a polyolefin, the tie sheet, which is itself a laminate, may have a first layer formed of a polyolefin which is compatible with the extruded elastomer and a second layer formed of a dissimilar material such as PVC with the layers of the tie sheet being joined by conventional adhesive. An outer layer may be adhered over the tie sheet.
U.S. Pat. No. 4,446,179 discloses a different type of laminated trim strip having an elongated molding formed from one of a wide variety of materials including PVC with a decorative surface of Mylar and an overcoat of cast plastic.
U.S. Pat. No. 4,533,510 discloses a method and apparatus for continuously co-extruding a sheet having two or more layers in a central portion of the sheet and only a single layer at the edge portions of the sheet. Under the invention therein disclosed, the widths of the center and edge portions may be accurately controlled and varied.
U.S. Pat. No. 4,094,947 discloses a process for co-extruding multiple layers of plastic material in which the thickness of the groups of layers may be varied. Under the process disclosed therein, the die head divides both first and second layers of material into multiple streams.
U.S. Pat. No. 4,128,386 discloses method and apparatus for extruding patterned sheets of differently colored thermoplastic resins which include the step of distributing additional color compositions outside of an extrusion duct of a basic color composition over a number of individual feed channels.
The disclosures contained in such references are hereby incorporated by reference.